I can't think of the worst movie I've ever seen, but I can remember the worst movie I've seen recently.
Birdemic: Shock and Terror was physically painful to watch. I was told forever that it's a must-see film that's so bad it's good. I mean, I loved The Room for it's ridiculousness, but Birdemic was a nightmare of epic proportions.
Imagine this: the quality, pacing and content of the movie was essentially "Hey, I made a video for Youtube and now I'm gonna put it on Youtube". That's the quality you were getting in acting and execution. I couldn't make it through 20 minutes without turning it off.